1. Field of the Invention
This invention relates to an apparatus which uses flow cytometry to classify and enumerate cells such as leukocytes, erythrocytes, epithelial cells, casts and bacteria contained in urine.
2. Description of the Prior Art
Examination of urine content has long been carried out and is still of great importance. For example, a screening test for kidney failure can be conducted based upon the presence of erythrocytes, leukocytes, epithelial cells, casts and bacteria in urine. Measurement of erythrocytes is important in terms of determining whether hemorrhage has occured in the tract from the slomerulus to the urethra of the kidney. The appearance of leukocytes is considered to be a possible indication of a kidney disorder such as pyelonephritis, and detection thereof is important in early discovery of inflammation and infection. Furthermore, by examining cast and erythrocyte morphology, the origin of such inflammation and infection, namely the abnormal parts of the body, can be surmised.
In this specification, the word "cell" shall be used as a generic term for an erythrocyte, epithelial cell, cast and bacterium.
Conventional methods of analyzing cells in urine include (a) visual examination based upon microscopy and (b) automatic measurement using a combination of a flat sheath flow and image processing technology.
Method (a) involves centrifuging a urine specimen, preparing a slide sample of the matter of sediment and observing, classifying and counting cells under a microscope.
Method (b), an example of which is disclosed in the specification of Japanese Patent Application Laid-Open (KOKAI) No. 57-500995 or USP 4,338,024, involves using a video camera to capture an image of a urine specimen made to flow as an extremely flat stream within a sheathing solution employed as an outer layer, and subjecting the still picture obtained to image processing, whereby the images of the cells in the specimen are extracted and displayed.
However, both of the foregoing methods exhibit certain drawbacks. Specifically, method (a) which relies upon a microscope entails considerable labor for such pre-treatments as centrifugal separation and staining. In addition, cells may be damaged in the centrifuging process and there are disparities in concentration from one specimen to another.
The apparatus which uses method (b) is itself high in cost owing to reliance upon image processing, and the processing speed is low. Furthermore, the advantage of automation afforded by the apparatus of method (b) merely displays the images upon roughly classifying the imaged components based upon their size, and it is required that classification process be performed by a human being while the display is observed. Thus, the automatic classification and enumeration of cell components is not possible.
Further, since the amount of the urine specimen measured according to the methods (a) and (b) is very small, a drawback is that casts, the discovery of the presence of which is very important, cannot be discovered in the urine sediment. Specifically, the low frequency of the presence of cast in such that usually only several tens thereof are present per milliliter.
Another problem is that since the types of components in urine sediment are numerous and differ widely in size from one specimen to another, and in view of the fact that the degree of cell damage can be considered to be large, it is understood that analysis of urine sediment is not possible using flow cytometry.
Still another problem is that a number of some cells such as bacteria in urine clumps to form a large cell diameter, thus making it difficult to distinguish between a clumping group of bacteria and a blood cell.